The largest evolutionary study on the coronavirus confirms the origin of Sars-CoV-2 from bats to humans

We have been living with an invisible enemy for over a year: the Sars-CoV-2 coronavirus, which is responsible for the Covid-19 pandemic and was previously unknown to the human species.

Some theories about how the new virus was transmitted to humans surfaced as early as 2019, with the hypothesis that it was a bat coronavirus that infected pangolins first and then humans based on closeness to sellers and customers these animals at Wuhan’s animal markets. where the first cases were recorded.

The World Health Organization (WHO) itself sent experts to Wuhan this year to find answers to this question. The report released by the organization in late March suggested the origins of bats, but the scientists found no evidence that Patient Zero was visiting a local animal market.

The largest evolutionary study on coronavirus has now confirmed the origin of Sars-CoV-2 from a bat coronavirus rather than pangolins and also warns of the importance of studying viruses in these animals as a global surveillance strategy for endemic diseases. and not only in health emergencies.

The research was carried out at the University of North Carolina’s Bioinformatics Research Center at Charlotte (UNCC) under the direction of Professor Daniel Janies from the same center. The first author is the Brazilian and bioinformatician Denis Jacob Machado, who is also a doctoral researcher at UNCC.

The scientific article was published last week in the journal Cladistics, best known for the evolutionary analysis of living things.

Many of the previous studies on coronaviruses have focused on some common genes of different species and, for example, did not provide determinative information about what type of host this virus is.

The study is innovative, besides the broad sample, as it presents the main annotations of the genomes that essentially organize the various genetic sequences of the coronaviruses into known and separable parts. For this purpose, a special tool was implemented to collect and compare these notes developed by Bioinformation. “It’s similar to deciding which house to rent: you compare the location of one house to another, but you don’t compare the color of one house to the number of rooms in the other. Locations are comparable; The color and number of rooms are different things, ”explains Machado.

“Without known genomes, evolutionary analyzes are limited to very similar genomes, e. B. apartments that are located in the same building, or a certain characteristic that these genomes have in common and that is easier to compare, e. B. the price between properties. In our analogy with houses, we can use it to pass on important information. “

To better understand how the study was conducted, phylogeny studies that seek to understand the evolutionary history of a group are performed using a range of data (e.g., the genome) of a particular group or a range of organisms (e.g., different species carried out by cats). We will hardly try to understand the origin and development of humans, for example by comparing our genome with that of horses.

In that sense, the evolutionary research published to date, sped up due to the health emergency, sinned both in terms of the number of species trapped and in terms of the use of weak data that could not adequately explain this story, says Machado.

“An inevitable difficulty in studying the evolution of the coronavirus is that there may be a mix of genes from different individuals [recombinação gênica]. Fortunately, only part of the coronavirus genome is affected by recombination events. By analyzing more genomes in a set, we were able to identify those events that cause noise when analyzed. It’s like a painting by Monet [Claude Monet, pintor impressionista]. Up close, the individual brushstrokes look like a stain without an outline. But when you zoom in and look at it, the brushstrokes organize and create the picture, ”he explains.

However, the analysis by Machado and his colleagues included more than 2,000 unique coronavirus genomes from four different genera of the subfamily Orthocoronavirinae: deltacoronavirus (DeltaCoV) and gammacoronavirus (GammCoV), typical of birds, and alphacoronavirus (AlphaCoV) and betacoronavirus ( (AlphaCoV) Beta that can infect humans.

Examples of beta coronaviruses that infect humans include Sars-CoV-2, Sars-CoV (responsible for the SARS epidemic between 2002 and 2003) and Mers-CoV (causing the respiratory syndrome in the Middle East), which range from bats to humans ;; HCoV-4408 and HCoV-OC43 (from cattle to humans) and HCoV-HKU1 (from rodents to humans). The alfacoronavirus HCoV-NL63 also started from bats to humans.

According to the biologist, who is one of the most important coronaviruses for human health, the study confirms that bats in the cases of Sars-CoV and Sars-CoV-2 were sources and also played a key role in the development of Mers-CoV. “Almost immediately after these animals were infected with the bat coronavirus, there were several transmission events between dromedaries and humans,” he explains.

The role of intermediate hosts in research was also assessed. “Our argument is that nothing indicates the need for an intermediate host [para o Sars-CoV-2]as it is clear that the infection of other mammals, such as civets [espécie de mustelídeo] and mink emerged in humans after the initial infection, illustrating the ability of coronaviruses to migrate between mammals of different species, ”he says.

The result of the research brings an important message: new events for the transmission of the coronavirus from animals to humans should occur in the near future without being able to predict when this will happen. “It’s important to invest in research [de forma] cataloging and describing the diversity of viruses in nature with the potential to infect humans, and that depends not only on a surveillance system but also on investment in science. “

“This research is difficult to fund and often neglected until, for example, a new pathogen comes from a natural source that was previously thought to be of little concern. When we talk about global efforts to monitor emerging diseases, we are also talking about building bridges that bridge the gap between basic and applied research. “, He says.

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